1. Field of the Invention
The invention relates to an electronic device having a housing for accommodating a carrier substrate and a filter device arranged in the housing for improving the electromagnetic sensitivity of the device, said carrier substrate being fitted with an electronic module and a conductor structure for making electrical connection with the electronic module.
2. Description of the Related Art
Shielding electronic devices against interference radiation which occurs in the high frequency range is required to ensure satisfactory functioning of electronic devices. Such interference suppression measures are usually provided in the interior of the electronic device.
German reference DE 299 02 505 U1 discloses a planar filter in which a capacitor is formed on a ceramic substrate. One side of the ceramic substrate is provided with the mass electrode and the other side with the signal electrodes of the capacitor. The signal electrodes form insular regions, which surround pin bushings of signal pins. Such interference suppression filters are used in electronic control devices in a motor vehicle, the interference suppression filter being arranged directly at the inlet of the plug connections in the housing.
It is disadvantageous here that during the mounting of this planar filter, satisfactory functioning of the planar filter is ensured only if a reliable electrical and/or capacitive connection to the housing is ensured to avoid undefined capacitance values.
It is an object of the present invention to provide an electronic device which has a filter device that is also suitable for mass production and which is easy to adjust.
The object of the present invention is achieved by a filter device formed by an electrical and/or capacitive connection of a first conductor surface of the conductor structure to an external first potential and by an electrical and/or capacitive connection of a second conductor surface of the conductor structure to a second electrical potential, the first and second conductor surfaces being arranged approximately opposite one another.
The present invention has the advantage that the filter device is an integral component of the carrier substrate and can be prepared at the time the printed circuit board is manufactured. When the first and second conductor surfaces are installed in the device, the conductor surfaces only need to be connected to the electrical potentials. The position of the filter formed by the first and second conductor surfaces is permanently predefined by the installation position of the printed circuit board. The mounting procedure does not require any additional adjustment measures such as occur when separate filter devices are used. This has the advantage that a customary printed circuit board which has a plurality of conductor tracks lying one on top of the other acts itself as a filter device.
In one embodiment of the present invention, the first electrical potential is a voltage which is supplied externally to the electronic module, and the second potential is that of the housing which is embodied so as to be electrically conductive.
In a further embodiment of the present invention, the part of the carrier substrate which comprises the filter device covers a housing opening through which a lead for supplying the first electrical potential to the interior of the housing engages.
The filter device can thus easily be positioned at the location where experience has shown that the greatest incidence of interference radiation is to be expected, and prevents, when mounted in accordance with the specifications, the ingress of high frequency radiation into the interior of the housing. This results in a device which can be handled particularly satisfactorily for mass production.
The first conductor surface of the filter device advantageously forms a first capacitor surface which surrounds the external lead, and a second conductor surface forms a second capacitor surface which is arranged above and/or below the first conductor surface, electrically insulated therefrom. If multilayer printed circuit boards are used, by simply electrically connecting the layers of different configuration it is possible to provide a filter device on which the electronic components are simultaneously arranged and provided with electrical contacts.
The external lead is advantageously formed by at least one plug-in element of a plug-in device which is arranged in or on the opening of the housing so as to cover it, the plug-in element being electrically connected to the first capacitor surface so as to engage into the carrier element through the opening.
In this way, a single pressing-in operation is effective for securing the plug a simultaneously making electrical contact with the capacitor electrode.
The use of a plug-in device with a plurality of plug-in elements makes it easily possible for the first capacitor surfaces, which are electrically insulated from one another and are associated with different plug-in elements, to be formed for each plug-in element in one conductor layer.
Such a structure can easily be manufactured during one operation when the printed circuit board is manufactured.
The filter device may be implemented in a particularly simple embodiment when the second conductor surface is embodied on the surface of the carrier substrate as an unstructured contact layer which bears partially against the electrically conductive housing. In this embodiment, the step of bringing about electrical connection to the second conductor surface is dispensed with. As a result of this measure, the housing itself acts as a second capacitor plate.
To form a further capacitor for the same plug-in element, the carrier substrate advantageously has two further conductor surfaces which lie one on top of the other and are electrically insulated from one another. The third conductor surface is electrically conducted to the plug-in element and the fourth conductor surface is electrically connected to the housing potential. As a result of this multilayer structure, which is limited solely by the conductor layers present in the carrier substrate, relatively large capacitance values for each plug pin may be implemented.
In one embodiment, the fourth conductor surface may also be implemented as an unstructured contact surface which is arranged on the second outer side of the carrier element, the unstructured contact surfaces which lie approximately one on top of the other are electrically connected to one another in the periphery of each plug-in element by a plurality of vias. As a result, a type of Faraday cage is formed around the plug-in element. That, along with the fact that an outer side of the carrier element bears tightly against the preferably electrically conductive housing, reliably prevents interference radiation from penetrating the interior of the housing.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.